As disclosed in U.S. Pat. No. 4,594,453 (Ranken et al.), it is known that various (hydrocarbylthio)aromatic amines are useful as intermediates in the preparation of biologically-active materials, polyurethanes, etc.; and they can be prepared by reacting an aromatic amine with an alkyl disulfide in the presence of a catalytic amount of a Lewis acid. The preferred catalysts of Ranken et al. are metal halides, such as aluminum chloride, boron trifluoride, boron trichloride, ferric chloride, and zinc chloride.
In the case of at least some aromatic amines, it has been found that the preferred catalysts identified by Ranken et al. have the disadvantages of effecting the desired hydrocarbylthiations at too slow a rate to be completely satisfactory and of sometimes providing too low a yield of product.
In U.S. Pat. No. 4,751,330 (Davis), various alkylthio-aromatic amines are prepared by reacting an aromatic amine with an alkyl disulfide in the presence of a metal or metal halide catalyst and iodine as a promoter. These reactions are noted to have higher reaction rates and/or higher yields than the prior art reactions discussed above.
However, even the improved process of Davis requires many hours to achieve satisfactory yields.